Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $169.74   8.803%   $184.6822   $184.68   $184.70   $184.70  
  Purchase #2 $172.84   6.585%   $184.2215   $184.22   $184.20   $184.20  
  Purchase #3 $16.27   9.705%   $17.849   $17.85   $17.85   $17.80  
  Purchase #4 $225.57   6.596%   $240.4486   $240.45   $240.45   $240.40  
  Purchase #5 $48.66   13.412%   $55.1863   $55.19   $55.20   $55.20  
  Purchase #6 $118.98   5.818%   $125.9023   $125.90   $125.90   $125.90  
  Purchase #7 $199.29   8.374%   $215.9785   $215.98   $216.00   $216.00  
  7 purchase totals = $951.35       $1,024.2684   $1,024.27   $1,024.30   $1,024.20